The present invention relates to an optical recording medium which has a wobbling groove extending along the recording tracks, on which signals are recorded in the form of changes in reflectance of organic dye-based recording material, while wobbling signals are being reproduced from the wobbling groove. The invention also relates to a master plate for use in manufacturing such an optical recording medium.
Optical discs have been put to practical use as optical recording media. Signals can be optically recorded on, and reproduced from, an optical disc. Known as such an optical disc is one on which signals can be written. This type of an optical disc (hereinafter referred to as xe2x80x9cCD-R) is used in so-called compact disc recordable systems. A CD-R is a rewritable optical disc made of organic dye-based material, on which signals can be recorded and from which signals can be reproduced.
The CD-R has a wobbling groove that extends along the recording tracks. A wobbling groove is a guide groove that meanders at a prescribed frequency. So meandering, the wobbling groove records signal components. It should be noted that a xe2x80x9cguide groovexe2x80x9d extends along a recording track to facilitate the tracking servo control that is performed by, for example, push-pull method.
In a CD-R, the sector data containing frequency-modulated, absolute time data is recorded in the form of signals (wobbling signals) represented by the wobbling groove (ATIP: Absolute Time In Pregroove). In the compact disc recordable system that uses a CD-R as recording medium, a recording-reproducing light beam is focused, forming a light spot at a wobbling groove. Wobble signals superimposed on carrier waves of, for example, 22.05 kHz are thereby detected from the wobbling groove. The wobble signals are frequency-modulated, thus generating a data stream that contains absolute time data.
With a system that records sector data containing the absolute time data, in the form of wobble signals, it is possible to record signals continuously. The system is therefore compatible with read-only optical discs, on which signals are recorded continuously. In a system wherein address data is recorded at the head of each sector, the absolute time data and the recorded data are spaced apart; namely, the signals recorded are discontinuous. Consequently, this system can hardly be compatible with read-only optical discs, on which signals are recorded continuously. By contrast, the first-mentioned system that records sector data containing the absolute time data, in the form of wobble signals can easily be rendered compatible with read-only optical discs.
Optical discs of the type mentioned above are now modified to record more signals, while having the same diameter as the existing standard optical discs. In other words, they are modified to record signals at higher densities. Moreover, it is proposed that CD-Rs be provided that can record signals at density two times or four times as high as the recording density of the existing standard CD-R.
To increase the recording density of an optical disc, it is advisable to reduce the track pitch, i.e., and the intervals at which the recording tracks are formed on the optical disc. If the track pitch is decreased, however, the recording-reproducing characteristics of the disc (jitter characteristic and the like) will be deteriorated.
Therefore, to provide two-time density CD-Rs and four-time density CD-Rs, i.e., optical discs having high recording density, it is necessary not only to reduce the track pitch, but also to implement sufficient recording-reproducing characteristics, such as jitter characteristic and the like.
A wobbling groove may be made in the surface of, for example, a CD-R, thus recording the absolute time data on the CD-R. In this case, it is desired that a wobble signal be efficiently reproduced from the wobbling groove.
In order to enhance the recording density of an optical disc, it is necessary, as described above, not only to reduce the track pitch, but also to achieve sufficient recording-reproducing characteristics, such as jitter characteristic and the like, so that wobbling signals and the like may be generated at adequately high level. (Note that the wobbling signals and the like are required to record signals on and reproduce signals from the recording tracks.)
The present invention has been made in view of the foregoing. An object of the invention is to provide an optical recording medium from which wobbling signals can be generated at sufficiently high level and which exhibits sufficient recording-reproducing characteristics, such as jitter characteristic and the like. Another object of this invention is to provide a master plate for manufacturing such an optical recording medium.
An optical recording medium according to this invention has recording tracks and a wobbling groove extending along the recording tracks. It is designed to record signals in the form of changes in reflectance of organic dye-based recording material, while reproducing a wobbling signal from the wobbling groove. The wobbling groove has a depth ranging from xcex/2.90 n to xcex/2.15 n. Here, xcex is the wavelength of a light beam applied to record and reproduce signals and n is the refractive index of medium existing between a surface to which the light beam is applied and surface in which the wobbling groove is made. The wobbling groove has a width Wg, and the recording tracks are arranged at a pitch Tp. The ratio of the width Wg to the track pitch Tp, Wg/Tp, falls within the range of 25.0% to 45.5%.
Since the wobbling groove has a depth and width specified above, the optical recording medium of the invention can provide a wobble signal that has a level high enough to record and reproduce signals even if the track pitch is decreased to enhance the recording density, and can reliably attain a practically adequate jitter characteristic. Hence, it is possible to record signals on this optical recording medium at high recording density.
In the optical recording medium according to the invention, it is desired that Ag/Tp should fall within the range of xc2x11.82% to xc2x13.18%, where Ag is the amplitude of the wobbling groove. Even if the wobbling groove has the depth and width specified above, a wobble signal may not be generated from the optical recording medium in the case where the amplitude of the wobbling groove is too small. Even if the wobbling groove has the depth and width specified above, the medium may fail to attain an adequate recording-reproducing characteristic such as jitter characteristic in the case where the amplitude of the wobbling groove is too large. Nonetheless, the optical recording medium of the invention can reliably provide a wobble signal and attains good recording-reproducing characteristic such as jitter characteristic, because the wobbling groove has the amplitude specified above.
A master plate according to the present invention is designed for use in manufacturing an optical recording medium. The optical recording medium has recording tracks and a wobbling groove extending along the recording tracks. The medium is designed to record signals in the form of changes in reflectance of organic dye-based recording material, while reproducing a wobbling signal from the wobbling groove, said master plate having a groove pattern that corresponds to the wobbling groove of the optical recording medium. The master plate has a groove pattern that corresponds to the wobbling groove.
The optical recording medium manufactured by the use of the master plate has a wobbling groove that has a depth ranging from xcex/2.90 n to xcex/2.15 n, where xcex is the wavelength of a light beam applied to record and reproduce signals and n is the refractive index of medium existing between a surface to which the light beam is applied and surface in which the wobbling groove is made. The wobbling groove has a width Wg, and the recording tracks are arranged at a pitch Tp. The ratio of the width Wg to the track pitch Tp, Wg/Tp, falls within the range of 25.0% to 45.5%. That is, the master plate has a groove pattern corresponding to the wobbling groove having the depth and width specified above.
Any optical recording medium manufactured by the use of the master plate can provide a wobble signal that has a level high enough to record and reproduce signals even if the track pitch is decreased to enhance the recording density, and can reliably attain a practically adequate jitter characteristic. Hence, it is possible to record signals on this optical recording medium at high recording density.
It is desired that the master plate have a groove pattern corresponding to a wobbling groove in which Ag/Tp may falls within the range of xc2x11.82% to xc2x13.18%, where Ag is the amplitude of the wobbling groove. If the ratio Ag/Tp falls within this range, the optical recording medium made by using the master plate will provide a wobble signal that has a level high enough to record and reproduce signals even if the track pitch is decreased to enhance the recording density, and will reliably attain a practically adequate jitter characteristic. It is therefore possible to record signals on this optical recording medium at high recording density.
As described above in detail, the optical recording medium according to the present invention can provide a wobble signal that has a level high enough to record and reproduce signals even if the track pitch is decreased to enhance the recording density, and can reliably attain a practically adequate jitter characteristic.
The master plate according to this invention can serve to manufacture an optical recording medium which can provide a wobble signal of a level high enough to record and reproduce signals even if the track pitch is decreased to enhance the recording density, and which can reliably attain a practically adequate jitter characteristic.